The most common and most likely answer to this crossword clue is the 6 plus 9 letter word SILVER MEDALLIST
I've seen this crossword clue in Financial Times
S
I
L
V
E
R
M
E
D
A
L
L
I
S
T
More clues leading to the result SILVER MEDALLIST
Buddy explains!

The straight part
We know that "runner-up" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case runner-up = silver medallist.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.